Power Supply Bench Testing Question

I hope this is the right section. I am trying to bench test a aftermarket radio and I was going to use this cheapo jump starter I have for power. I hooked my multimeter up to the jump starter and got a reading of about 13v. I know I am supposed to connect both the red and yellow to the positive (+) and the black to the negative (-) and it should start. However, at 13v, is it safe to hook the radio up or should I wait until it goes down below 12v? It being a cheapo jump starter it doesn't hold a charge that well.

A 12V car radio should handle up to 16V.
Cars are rarely as low as 12V - when driving/charging, they normally range between 13.6 & 14.5V.

It is confusing.
A "12V" battery is normally 12.67V fully charged; can be 13.6V after charging (with surface charge remaining); is considered fully discharged at ~11.4V unloaded/open circuit but that may mean 10.6V at rated loads, and cranking may dip them as low as 9 or 8 Volts.

Hence an (or my?) oldskool common design target was that devices should work between 8V and 16V steady-state - or at least not be destroyed between those ranges!